SciELO - Scientific Electronic Library Online

 
vol.65 issue2A comparative study in AA4006 alloy strips produced by twin roll caster and direct chill processes: microstructure and crystallographic textureDevelopment of a metallic material selection model by applying a logistic approach : the case of a company in the mining metallurgist sector author indexsubject indexarticles search
Home Pagealphabetic serial listing  

Rem: Revista Escola de Minas

Print version ISSN 0370-4467

Abstract

HUPALO, Marcio Ferreira; RAMOS, Daniele da Silva; RABELO, Alexsandro  and  LIMA, Nelson Batista de. Kinetic and microstructural aspects of incomplete bainite transformation in austempered ductile irons. Rem: Rev. Esc. Minas [online]. 2012, vol.65, n.2, pp. 217-224. ISSN 0370-4467.  http://dx.doi.org/10.1590/S0370-44672012000200010.

This work aimed at studying the kinetic aspects of the incomplete bainite transformation of ductile cast iron containing 2.36 and 2.68% silicon (in wt %). Samples were initially austenitized at 900°C during 90 minutes and then austempered at 320 and 370°C in times ranging from 1.5 to 60 minutes. Microstructural characterization was performed by light optical microscopy (LOM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and Vickers microhardness tests. A LOM-based method for transformed fractions quantification has been developed. Due to its high silicon content, both alloys presented the bainite transformation stasis phenomenon. Samples austempered at 320°C displayed more refined microstructures and higher transformed volume fractions at the reaction stasis beginning. Low resolution is the main drawback for using light optical microscopy in the phase quantification. Transformed volume fractions determined by XRD showed smaller values than those obtained by LOM, mainly for the lower austempering temperature. Kinetic transformation curves have been determined for all studied conditions. The Johnson-Mehl-Avrami-Kolmogorov (JMAK) model was used to study the incomplete bainite transformation kinetics. Avrami exponents varied from 0.15 to 0.67.

Keywords : Austempered ductile iron; phase transformations; microstructure; retained austenite; bainitic ferrite.

        · abstract in Portuguese     · text in Portuguese     · pdf in Portuguese